DESCRIPTION (Applicant's Description) Considerable controversy exists regarding the optimal strategy to evaluate the colon. The most common tests used to image the colon include air contrast barium enema and colonoscopy, each of which is associated with its own sets of benefits and limitations. Accuracy, cost and patient acceptance are all critical issues. Disagreement over which test is most desirable in specific situations remains because available studies have not fully addressed all of the relevant issues. We have performed a pilot study to begin to address the issue of diagnostic accuracy of air contrast barium enema compared to colonoscopy. We found complete concordance of both studies in patients with carcinoma, however, the sensitivity of air contrast barium enema compared to colonoscopy was less for adenomas > 1 cm in size, although diverticula appeared to critically confound the interpretation of air contrast barium enema. We have also examined in a pilot study, patient experience during air contrast barium enema and colonoscopy; colonoscopy was found to be more painful than air contrast barium enema. Computed tomographic colonography (otherwise known as virtual colonoscopy), has been recently introduced as an alternative colonic imaging modality. We have also performed preliminary work to address the issue of diagnostic accuracy of computed tomographic colography compared to colonoscopy. We find that this modality has a relatively high sensitivity when compared to colonoscopy, on the same order as that of air contrast barium enema. Although virtual colonoscopy has therefore generated considerable enthusiasm, a consensus of its diagnostic accuracy is currently unavailable and moreover, its sensitivity compared to air contrast barium enema is entirely unknown. This application therefore proposes to study the relative accuracy of air contrast banum enema, colonoscopy and virtual colonoscopy. We will also perform analyses to determine how the tests are viewed by patients and to determine which is the most cost-effective approach for evaluation of patients with fecal occult blood, the major indication for colonic imaging. The information gained from this study is expected to form the basis for national policy and decision making with reward to colonic imaging tests.